Commentary calcium and phosphates am j health-syst pharm—vol 65 jan 1, 2008 73 commentary calcium and phosphate compatibility: revisited again. Serum phosphate 1.5-2.4 mg/dl – may be considered a moderate decrease and typically does not give rise to clinical signs and symptoms. Conversions tables used in fertigation and hydroponics for element and nutrient forms; ppm to meq/l and vise versa. all conversions on one page!.